1. Field of Invention
The present invention relates to a processing method and device for an image, and, in particular, to a processing method and device for a halftone image.
2. Related Art
Digital halftone technology is an image processing method which simulates a continuous tone image by varying dots in size or in spacing. Adding additional noise and error diffusion are two commonly used methods in the digital halftone technology.
Adding additional noise is to add noise into images before quantization. The added noise can destroy the monotony resulted from the fixed gray level, such that the halftone image can be similar to the original image.
Error diffusion is another way of halftoning in which the quantization residual is distributed to neighboring pixels that have not yet been processed. The halftone image that is processed with the error diffusion is better than that of dithering in quality. However, the error diffusion method may cause the worms in images and requires significant computational resources to implement.
Moreover, the conventional halftoning technology has a problem of “start-up delay” occurred near edges or boundaries of the image. This is because that the gray values of several initial pixels are lower than the error diffusion threshold value such that no dots are added into the image.
Therefore, it is an important object to provide a processing method and device for fast halftoning image and providing good image quality.